On the correlation of the activity coefficients in aqueous electrolyte solutions using the K-MSA model

The objective of this work is to extend the Kelvin mean spherical approximation (K-MSA) model to correlate the mean and individual ionic activity coefficients for symmetric and asymmetric electrolyte solutions at different concentrations and at different temperatures. Revised values of the parameters for the mean and individual ionic activity coefficients of 1:1 electrolytes and new values of the parameters for the mean ionic activity coefficients of asymmetric electrolytes are presented. The effect of the short-range electrostatic term (P-n) at different size ratios of the ions is examined. Assuming a constant anion diameter and a composition-dependent diameter for the cation, the K-MSA model gives realistic cation-hydrated diameters, in comparison with their crystallographic Pauling diameters. Notably, for both symmetric and asymmetric electrolytes, the like and unlike ionic radial distribution function at contact value are positive over all of the concentration and temperature ranges studied. The results obtained from the K-MSA model compare favorably with those obtained from the Boublik-Mansoori-Carnahan-Starling-Leland mean spherical approximation and Pitzer models for the mean ionic activity coefficients and with those obtained with the Khoshkbarchi-Vera model for the individual ionic activity coefficients.